The invention concerns a method for evaluating radio links in a communication network, such as (but not limited to) an IEEE 802.11 network.
In a wireless network, two devices communicating over a radio link may be required to dynamically configure their transmission parameters. Such parameters may include in particular the emitter's active antenna sector or element in case of multi-sectored antenna, the automatic gain control settings, the frequency offset, the physical mode, the data rate or other parameters. Antennas comprising a plurality of elements are frequently encountered nowadays. One of the most popular antennas is the space diversity antenna of order 2, comprising two simple elements spaced by lambda/2 to reduce the probability of having both elements in a fading region.
Selecting the proper parameters has a direct influence on the robustness and the overall performance of a radio link. Indeed, it is known that wireless networks in the 2 to 5 GHz area are sensitive—among other factors—to people moving within a room. This movement induces significant changes of the channel characteristics. As a result, the selection of the active receiver antenna element may need to be updated. An update period of 100 Hz can be considered as sufficient compared to the speed of movement of people.
The European patent application 01402592.8, filed on Oct. 10, 2001 in the name of Thomson Licensing S. A. and entitled ‘Methods and devices for radio link adaptation’ describes methods and devices adapted to carry out radio link evaluation in a centralized network, such as a wireless network based on ETSI BRAN HiperLAN 2. Another European patent application filed on the same day as the present application in the name of Thomson Licensing S. A. and entitled ‘Method for radio link adaptation in a non-coordinated network’ concerns non-coordinated networks such as networks based on IEEE 802.11.
In these applications, receiver mobile terminals trigger the transmission of predetermined test data from known transmitter mobile terminals, in order to carry out the evaluation of the radio link with different transmission parameter values (antenna element, physical mode . . . ).
A receiver terminal can receive data from several transmitter terminals, and may be required to continuously evaluate links from all transmitter terminals in order to avoid fading. The probing may generate a significant amount of traffic on the network, and may also use a significant part of the receiver terminal's processing resources.